Multiverse

"[The Many-worlds interpretation is the] only completely coherent approach to explaining both the contents of quantum mechanics and the appearance of the world."

-Hugh Everett III

In physical cosmology, the multiverse is an infinite group of multiple universes including the universe in which we live. The multiverse theory states that they're a infinite number of universes coexisting with ours on parallel dimensional planes, unlike the planes of existence, including the Astral Plane. Each universe has a deviated reality from each universe from its Point of Divergence (POD), thus creating any alternate history eventuality.

In Davis Rainier, the multiverse is introduced on Season 5.